A known brake control apparatus for a vehicle is disclosed in a U.S. Pat. application Ser. No. 5,372,409 which corresponds to a Japanese Patent Laid-open Application No. 2(1990)-241863. This known brake control apparatus includes a tandem hydraulic master cylinder capable of generating a master cylinder hydraulic pressure to be supplied to a wheel brake cylinder, a vacuum-suspended booster for activating the master cylinder, and an electromagnetic valve means for activating the booster. When a driving wheel is idly spinning, the master cylinder hydraulic pressure is generated in response to an automatic operation of the booster by the electromagnetic valve means. The master cylinder hydraulic pressure is supplied to the driving wheel (i.e. a controlled wheel) spinning irrespectively of operation of a brake pedal, wherein braking force can be applied to the controlled wheel. In this case, a traction control can be executed. While the traction control has been executed, a non-controlled wheel, which is not driven, has been disconnected from the master cylinder via an anti-lock modulator assembly.
As described above, while the traction control has been executed, the non-controlled wheel has been always disconnected from the master cylinder. Therefore, when the brake pedal is depressed by a driver under the traction control, a vehicle deceleration can not be generated corresponding to the brake pedal depression. Further, when the above-described brake control apparatus is applied for use in other hydraulic pressure control devices including a steering control device, and so on, the same problem may occur.
The present invention therefore seeks to provide an improved brake control apparatus capable of generating a vehicle deceleration corresponding to a brake pedal operational amount and of improving a brake pedal operating feeling applied to a driver when the brake pedal is operated while a hydraulic pressure control has been applied to a controlled wheel.